function range(firstnum, lastnum, step){
  var mas=[];
  if (step)
    var i = step;
  else
    i = 0;
  if (step<0){
    mas.push(firstnum);
    for(i; i>(-(firstnum+step)); i--){
    mas.push(firstnum+i);}}
  else{
    for(i; i<lastnum; i++){
    mas.push(firstnum+i);}}
  return (mas);}

function sum(mas){
  var summa = 0;
  for(var i=0; i < mas.length; i++){
  summa+=mas[i];}
  return summa;}


console.log(range(1, 10));
// → [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]
console.log(range(5, 2, -1));
// → [5, 4, 3, 2]
console.log(sum(range(1, 10)));
// → 55